The Oxidation Behavior of Spark Plasma Sintered Ti-48Al Alloys

Titanium aluminide (TiAl)-based alloys are lightweight intermetallic compounds used in critical high temperature structural applications, such as jet engine components. However, its applications are limited by its inadequate high temperature oxidation resistance. The as-cast microstructure is lamellar, with alternating plates of γ-TiAl and α₂-Ti₃Al phases. On the other hand, the spark plasma sintering (SPS) process produces a non-lamellar microstructure of nanosized equiaxed grains of the γ-TiAl and the α₂-Ti₃Al phases. In this work, we study the oxidation resistance of both of these microstructures. Oxidized SPS samples form a TiO₂-Al₂O₃-TiO₂ layer structure. The poorer oxidation resistance of SPS samples is due to the larger α₂-Ti₃Al phase content and greater Ti migration to the surface induced by sintering porosity. There is a lower mass change and better oxidation resistance of mixed elemental powder-based SPS samples compared to ball-milled powder-based SPS samples. Thus, there is a significant difference in the oxidation kinetics of SPS and as-cast samples, with the improved oxidation resistance of the as-cast samples found to be resulting from the formation of a uniform homogeneous Al₂O₃ layer.